Experimental evidence for the critical wavelet transform level in multi-scale roughness decomposition of rock joints

• Published in: International journal of rock mechanics and mining sciences (Oxford, England : 1997) England : 1997), 2024-03, Vol.175, p.105662, Article 105662
• Main Authors: Yong, Rui, Zhong, Zhen, Li, Yingchun, Du, Shigui, Wang, Changshuo, Huang, Lei
• Format: Article
• Language: English
• Subjects: Direct shear test; Joint roughness; Multi-order; Shear strength; Wavelet transform level
• ISSN: 1365-1609; 1873-4545
• DOI: 10.1016/j.ijrmms.2024.105662

Shear behaviour of rock joints is highly affected by multi-order roughness and the mechanical involvements of each-order roughness in shear are different. Quantitative decomposition of total roughness into waviness (first-order) and unevenness (second- order) can be achieved by the well-accepted wavelet analysis; the decomposition quality depends heavily on the critical wavelet transform level (cWTL) at which the unevenness component is completely excluded from the total roughness while the waviness remains unimpaired. However, determination of the cWTL has been either empirical or based on pure statistical analysis of the joint morphology without a solid mechanical foundation. Here, we experimentally determined the cWTL by conducting direct shear tests on joint specimens profiled of serial WTLs with the aid of 3D printing and 3D scanning techniques. Through the joint analysis of mechanical data and quantified morphological variation, we found that the peak shear strength, shear strength component partition and shear-induced damage all experienced noticeable transition from WTL at 5 to 6 under a wide range of normal stress regimes, evidencing that the cWTL is 6, consistent with the one acquired from statistical analysis. Our conclusion provides a guiding value of the cWTL for investigating the roles of multi-scale roughness in rock joint shear.